Heliostat joint

ABSTRACT

A heliostat includes a joint with a range of motion in both elevation and azimuth of more than 90 degrees.

The present disclosure claims priority to U.S. Provisional PatentDisclosure Ser. No. 61/089,843, filed Aug. 18, 2008.

BACKGROUND

The present disclosure relates to a heliostat, and more particularly toa joint therefor. Current heliostats may have a relatively limited rangeof motion both in azimuth as well as in elevation. The relativelylimited range of motion may require configuration changes for bestoperation at different field positions and at different latitudes. Thismay result in the use of different heliostat configurations in differentfields or even in different parts of the same field to focus the sun'senergy on the receiver.

The relatively limited range of motion may also require some heliostatsto reposition themselves 180 degrees at specific times during the day tocontinue tracking the sun. This action typically requires approximately15 minutes during which the sun's energy is not captured.

SUMMARY

A heliostat according to an exemplary aspect of the present disclosureincludes a joint with a range of motion in both elevation and azimuth ofmore than 90 degrees.

A heliostat according to an exemplary aspect of the present disclosureincludes a pedestal which defines a longitudinal axis, the pedestaldefines a first radius. A first link is movably mounted to the pedestalabout a first axis. A second link movably mounted to the first linkabout a second axis, the second axis displaced from the longitudinalcenterline by at least the first radius.

A heliostat according to an exemplary aspect of the present disclosureincludes a joint having a first member and a second member, wherein thefirst member has an axis of rotation that is skew to an axis of rotationof the second member, wherein the axis of the first member is offset afirst distance from the axis of the second member, and wherein thesecond member has a radial length about the second axis at leastapproximately ½ of the first distance.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art fromthe following detailed description of the disclosed non-limitingembodiment. The drawings that accompany the detailed description can bebriefly described as follows:

FIG. 1 is a general schematic view of a solar power tower system for usewith the present invention;

FIG. 2 is a perspective view of a heliostat;

FIG. 3A is a side view of a heliostat with the heliostat array in afirst position;

FIG. 3B is a top view of a heliostat with the heliostat array in asecond position;

FIG. 4 is a perspective view of a first link for a joint for theheliostat;

FIG. 5 is a perspective view of a second link for a joint for theheliostat;

FIG. 6 is a perspective view of another embodiment of the first link fora joint for the heliostat;

FIG. 7A is a side view of a heliostat with the heliostat array in thefirst position illustrating a drive system;

FIG. 7B is a top view of a heliostat with the heliostat array in asecond position illustrating a drive system;

FIG. 8 is a top expanded view of the drive system; and

FIG. 9 is a side expanded view of the drive system.

DETAILED DESCRIPTION

Referring to FIG. 1, a solar power tower system 20 includes a highconcentration central receiver system 22 having a receiver 24 coupled toa tower structure 25 at a predetermined height above ground to receivesolar radiation S from a multiple of sun-tracking mirrors or heliostats26. Molten salt or other thermal transfer fluid is communicated from acold storage tank system 28 through the central receiver system 22 andheated. The heated thermal transfer fluid is then communicated to a hotstorage tank system 30. When power is required, the hot thermal transferfluid is pumped to a steam generator system 32 that produces steam. Thesteam drives a steam turbine/generator system 34 that createselectricity for communication to a power grid. From the steam generator,the thermal transfer fluid is returned to the cold storage tank system28 for storage until reheated in the central receiver system 22 whilethe steam is recovered through a condenser system 36. It should beunderstood that although a particular component arrangement is disclosedin the illustrated embodiment, any arrangement which makes use ofheliostats will also benefit from the present disclosure.

Referring to FIG. 2, the heliostat 26 generally includes a pedestal 40,a joint 42, a frame assembly 44, and a heliostat array 46. The pedestal40 supports the joint 42 to permit articulation of the frame assembly 44and thus the heliostat array 46 to track the sun and focus the solarradiation S as required.

Referring to FIG. 3A, the pedestal 40 may be a generally cylindricalcolumn which defines a longitudinal centerline A and a radius r1 (FIG.3B). A semi-spherical cap 48 in the disclosed, non-limiting embodimenttops the pedestal 40.

The joint 42 generally includes a first link 50 and a second link 52.The first link 50 includes a first arcuate arm 54 with end pivots 54A,54B and a second arcuate arm 56 with end pivots 56A, 56B. The end pivots54A, 54B, as illustrated define an initial elevation axis B and the endpivots 56A, 56B defines an initial azimuthal axis C (also illustrated inFIG. 4). The end pivots 54A, 54B are oriented relative the end pivots56A, 56B such that axis B is transverse to axis C. In one non-limitingembodiment axis B is perpendicular to axis C.

The second link 52 includes an arcuate arm 58 with end pivots 58A, 58B(FIG. 5) which engages the end pivots 56A, 56B of the first link 50(along axis C). Alternatively, the first link 50′ includes a single endpivot 56C (FIG. 6).

The first link 50 is movably mounted to the pedestal 40 about axis B.The second link 52 is movably mounted to the first link 50 about axis C.That is, axis C is offset by at least the column radius r1 relative tothe longitudinal centerline A by axis B to achieve a significant freedomof motion. The second link 52 positions the heliostat array 46 at leastan additional radius r1 from axis C to provide essentially unrestrictedazimuth and elevation motion of the heliostat array 46 relative to thepedestal 40. By using the elevational axis B to achieve the offset, thejoint 42 provides a significant range of motion in both elevation andazimuth. In one non-limiting embodiment, the range of motion is morethan 90 degrees and typically approximately 180 degrees in bothelevation and azimuth. It should be understood that the heliostat array46 may be mounted asymmetrically as desired to optimize load and otheroperating characteristics and requirements.

Through the unique combination of kinematics, a full range of smooth andcontinuous motion with no singularity conditions is achieved. The rangeof motion avoids any unique non-sun gathering maneuvers.

Referring to FIG. 7A, a drive system 70 attached between the pedestal 40and the heliostat array 46 at two points e, f on the heliostat array 46defines the orientation and position of the heliostat array 46. Thedrive system 70 generally includes two drive rods 72A, 72B such as leadscrews attached between the heliostat array 46 through mounts 74A, 74Band the pedestal 40 through offset aims 76A, 76B (FIG. 7B).

The drive system 70 adjusts the heliostat array 46 relative to thepedestal 40 to provide articulation to utilize the range of motionprovide by the joint 42. The joint 42 essentially provides one point gin space for the heliostat array 46. By defining the two other points e,f as represented by the mounts 74A, 74B the definition and orientationof the heliostat array 46 plane is established. In this manner, there isno singularity point and no need to significantly realign the azimuth tocontinue tracking the sun. Instead, sun tracking is accomplished in asmooth and continuous manner.

Each of the drive rod 72A, 72B are attached to the mounts 74A, 74Bthrough joints 78A, 78B such as a ball-joint or U-joint to provide auniversal connection therebetween. The mounts 74A, 74B support therespective joints 78A, 78B to permit rotation and articulation of therespective drive rod 72A, 72B to position the heliostat array 46.

Referring to FIG. 8, each offset arm 76A, 76B generally includes ashoulder 80, an arm 82, a forearm 84, a rotational bearing 86, a wristrotator 88 and a drive motor 90. A pivot 92 between the shoulder 80 andthe arm 82 permits movement of the arm 82 in a plane P transverse to thepedestal 40 and generally parallel to ground G (FIG. 7A). It should beunderstood the plane P may be alternatively oriented.

The wrist rotator 88 is mounted to the forearm 84 through the rotationalbearing 86 such that the wrist rotator 88 may rotate about the forearm84 (illustrated schematically by axis F and arrow F). The rotationalbearing 86 may essentially include a sleeve which permits rotation F.

The wrist rotator 88 includes a turntable 96 which permits rotation(illustrated by arrow W) of the drive motor 90 and thus the drive rod72A about an axis W (also illustrated in FIG. 9). That is, the wristrotator 88 supports the drive motor 90 through which the drive rod 72may be extended and retracted along axis Y through, for example, athreaded engagement with the lead screw. It should be understood thatother drive motors such as linear electric motors or other telescopicarrangements may alternatively or additionally be provided. Theturntable 96 may include rotational couplings to communicate electricalpower and controls signals to the respective drive motor 90.

The shoulder 80, arm 82 and forearm 84 provide an offset to provide fullmotion and avoid overextension of the drive rod 72A, 72B. The arm 82 andforearm 84 may each be of a length which is at least equivalent to theradius r1. The arm 82 and forearm 84 may alternatively be of a longer orshorter length dependant in part on whether more or less than a 180degree range of motion is to be provided. The drive rods 72A, 72B may bemaintained in tension when extended and only experience compressiveloading when at reduced extension.

The joint 42 facilitates an extended operational range for the heliostat26 with a robust drive system 70 for effective control and actuation ofheliostat 26. Unique maneuvers are avoided and relatively uncomplicatedand reliable hardware supports the heliostat array 46.

It should be understood that like reference numerals identifycorresponding or similar elements throughout the several drawings. Itshould also be understood that although a particular componentarrangement is disclosed in the illustrated embodiment, otherarrangements will benefit herefrom.

Although particular step sequences are shown, described, and claimed, itshould be understood that steps may be performed in any order, separatedor combined unless otherwise indicated and will still benefit from thepresent disclosure.

The foregoing description is exemplary rather than defined by thelimitations within. Various non-limiting embodiments are disclosedherein, however, one of ordinary skill in the art would recognize thatvarious modifications and variations in light of the above teachingswill fall within the scope of the appended claims. It is therefore to beunderstood that within the scope of the appended claims, the disclosuremay be practiced other than as specifically described. For that reasonthe appended claims should be studied to determine true scope andcontent.

1. A heliostat comprising: a joint with a range of motion in bothelevation and azimuth of more than 90 degrees.
 2. The heliostat asrecited in claim 1, further comprising a pedestal to which said joint ismounted, said pedestal defines a first radius, said joint includes anoffset in which a heliostat array azimuthal axis of rotation isdisplaced at least said first radius from said pedestal longitudinalaxis.
 3. The heliostat as recited in claim 1, wherein said jointprovides a range of motion in both elevation and azimuth ofapproximately 180 degrees.
 4. The heliostat as recited in claim 1,wherein said joint includes no singularity point.
 5. The heliostat asrecited in claim 1, further comprising a drive system which positions aheliostat array relative to a pedestal.
 6. The heliostat as recited inclaim 5, wherein said drive system defines two points on said heliostatarray and said joint defines one point on said heliostat array.
 7. Theheliostat as recited in claim 6, wherein said two points are defined inpart by a respective drive rod.
 8. The heliostat as recited in claim 7,wherein each of said respective drive rods includes a lead screw.
 9. Theheliostat as recited in claim 7, wherein each of said respective driverods are mounted to said pedestal through an offset arm structure.
 10. Aheliostat comprising: a pedestal which defines a longitudinal axis, saidpedestal defines a first radius; a first link movably mounted to saidpedestal about a first axis; and a second link movably mounted to saidfirst link about a second axis, said second axis displaced from saidlongitudinal centerline by at least said first radius.
 11. The heliostatas recited in claim 10, wherein said first axis is a longitudinal axis.12. The heliostat as recited in claim 11, wherein said second axis is anazimuthal axis.
 13. The heliostat as recited in claim 10, wherein saidsecond axis is perpendicular to said first axis.
 14. The heliostat asrecited in claim 10, further comprising a heliostat array mounted tosaid second link.
 15. The heliostat as recited in claim 14, furthercomprising a drive system which positions said heliostat array relativeto a pedestal.
 16. The heliostat as recited in claim 15, wherein saiddrive system includes two points attached to said heliostat array, saidtwo points defined in part by a respective drive rod.
 17. A heliostatcomprising: a joint having a first member and a second member, whereinthe first member has an axis of rotation that is skew to an axis ofrotation of the second member, wherein the axis of the first member isoffset a first distance from the axis of the second member, and whereinthe second member has a radial length about the second axis at leastapproximately ½ of the first distance.
 18. The heliostat as recited inclaim 17, wherein said radial length is at least equal to said firstdistance.
 19. The heliostat as recited in claim 17, wherein said jointprovides a range of motion in both elevation and azimuth greater than 90degrees.
 20. The heliostat as recited in claim 17, wherein said jointprovides a range of motion in both elevation and azimuth ofapproximately 180 degrees.